Switch adapting toys - changing switching mechanisms

Thread Starter

Sstanier

Joined Mar 4, 2019
17
Hi folks,
This is my first move from lurking. I switch adapt standard off the shelf battery operated toys so they can be operated by children with severe disabilities with a simple push button style switch connected by a 3.5mm mono jack. It’s very much “learn as you go” because I don’t have any electronics training (which also means really technical answers are going to go right over my head)
The question I have is: I am coming across toys which operate by LDR (for example). I am assuming the type of switch activation required is determined by the circuit board?
Is there a way I can change the switching mechanism so it can be operated by another switch type? Space is always an issue as most of them are like trying to work on an elephant in a shoebox.
Many thanks
 

djsfantasi

Joined Apr 11, 2010
6,506
Hi folks,
This is my first move from lurking. I switch adapt standard off the shelf battery operated toys so they can be operated by children with severe disabilities with a simple push button style switch connected by a 3.5mm mono jack. It’s very much “learn as you go” because I don’t have any electronics training (which also means really technical answers are going to go right over my head)
The question I have is: I am coming across toys which operate by LDR (for example). I am assuming the type of switch activation required is determined by the circuit board?
Is there a way I can change the switching mechanism so it can be operated by another switch type? Space is always an issue as most of them are like trying to work on an elephant in a shoebox.
Many thanks
Let’s say it’s possible, but not necessarily simple. An on/off switch can simply be paralleled. But your LDR operated toy may be more difficult. It depends on how the LDR is being used.
 

Thread Starter

Sstanier

Joined Mar 4, 2019
17
Let’s say it’s possible, but not necessarily simple. An on/off switch can simply be paralleled. But your LDR operated toy may be more difficult. It depends on how the LDR is being used.
Thank you. Can you elaborate on how to parallel an on/off switch? This toy is a crocodile and wasn’t working. It had a small round black “spout” on his nose which contained the LDR in a small black housing. I presume you touch the spout to affect the light and activate the toy. I am going to get a new one today to see if replacing it will at least get the toy operating. Then go from there.
It’s not the first toy I have come across with a switch type I couldn’t modify. One had a switch that had to be tapped (flicking it activated it, but pressing it didn’t) - I hadn’t seen it before and still don’t know what type of switch that is.
 

ArakelTheDragon

Joined Nov 18, 2016
1,350
Do you know how to measure with a multimeter? If its with an LDR it gets turned on or off based on light and voltage. When the light increases/decreases the voltage over the LDR changes.

You will have to at least be able to post and understand simple circuits.

Here is a simple LDR project.
 

Thread Starter

Sstanier

Joined Mar 4, 2019
17
Do you know how to measure with a multimeter? If its with an LDR it gets turned on or off based on light and voltage. When the light increases/decreases the voltage over the LDR changes.

You will have to at least be able to post and understand simple circuits.

Here is a simple LDR project.
Thanks. I understand how an LDR works - I was just trying explain where and how it was in this particular toy. I apologise for not being terribly technical in my explanations. My question is that I don’t want the toy to switch on and off with light because as long as that is the switching mechanism, the toy can’t be adapted for use with the various disability switches so can I change the mechanism given that I have to do it with the existing circuit board?
 

Thread Starter

Sstanier

Joined Mar 4, 2019
17
Do you know how to measure with a multimeter? If its with an LDR it gets turned on or off based on light and voltage. When the light increases/decreases the voltage over the LDR changes.

You will have to at least be able to post and understand simple circuits.

Here is a simple LDR project.
Or perhaps another way to ask is - is it possible to just close the circuit (and if so, how?) and then just use a battery interruptor as on/off? I don’t typically use battery interruptors because I think they are a tacky way to adapt a toy but this would be an exception if I can’t find any other work around.
 

Bernard

Joined Aug 7, 2008
5,556
In many cases some form of latching is required like in the case of the vibrator switch where
just a very short contact is made. Then a block out time may be required to prevent multiple
activations, like bounce protection on a switch.
The big problem is to define how toy is to be controlled, hard wire, remote, or direct contact, then what are input requirements.
 
Last edited:

Thread Starter

Sstanier

Joined Mar 4, 2019
17
In many cases some form of latching is required like in the case of the vibrator switch where
just a very short contact is made. Then a block out time may be required to prevent multiple
activations, like bounce protection on a switch.
The big problem is to define how toy is to be controlled, hard wire, remote, or direct contact, then what are input requirements.
Vibrator switch - that’s one I didn’t know and don’t have any of. I will definitely look into them and have a play and learn.

I think I have found the solution so I will give it a test run tomorrow and see how it goes. I bought some LDRs as I didn’t have any so will build some practice circuits to better understand them - I only had phototransistors. Thanks for the help.

The forum is great - I don’t know how I happened upon the thread (from 2013) but it answered another question I had been pondering - how to randomly activate switches in a toy that has several. Another thing I will be giving a test run as the schematics were given and I happen to already have the components so I just have to make and test it.
 

jpanhalt

Joined Jan 18, 2008
9,731
Are you asking about a push on/push again off button switch? As mentioned, there are various latching mechanisms and/or circuits for doing that. For example a single chip like the MAX16054 (https://datasheets.maximintegrated.com/en/ds/MAX16054.pdf ) can do the latching function. Note, it controls another switch and does not supply appreciable power itself.

Switches in parallel, like @djsfantasi suggested, give an inclusive OR function (one or more "on" gives "on"). Of course, the LDR switch could just be removed from the circuit (remove one of its connections) so only the alternative push button works.

@Sstanier : Sorry cross posted.
 

Thread Starter

Sstanier

Joined Mar 4, 2019
17
Are you asking about a push on/push again off button switch? As mentioned, there are various latching mechanisms and/or circuits for doing that. For example a single chip like the MAX16054 (https://datasheets.maximintegrated.com/en/ds/MAX16054.pdf ) can do the latching function. Note, it controls another switch and does not supply appreciable power itself.

Switches in parallel, like @djsfantasi suggested, give an inclusive OR function (one or more "on" gives "on"). Of course, the LDR switch could just be removed from the circuit (remove one of its connections) so only the alternative push button works.

@Sstanier : Sorry cross posted.
Unfortunately this particular toy has no other switching - it’s just the LDR - which is why I have battled with it. If it had a push button it would be really simple.

The switch mechanism in the toy can be on/off or, in particular situations where we are trying to teach the child to associate the external switch with the toy, normally as their introduction to adaptive technology, I set the switching so the toy will only operate while the switch is being pressed. But I have to make sure they are not toys that once you activate the switch it will run through a timed action until it’s finished, regardless of whether the switch is pressed again or not. In others, repetitive pressing will move through a series of options such as a toy having 5 songs and the child can keep pressing until they get to the one they want.

And because I don’t know what you know, the external switches for these kids are usually large arcade button style. The switch function doesn’t require power but I also make the switches and some are recordable so a message can be played when the switch is pressed, or are lit with LEDS because a lot of these children have vision impairment as well so those functions require power - but remove the batteries and the switch still functions. Which isn’t the case with commercially available ones with lights/messages etc, those it’s no power = no switch.

I don’t want to run before I can walk so while I have built a few bits and pieces I am trying to just work with the toys as they are for now. I have found some electronics training I can do, but the semester doesn’t start til later in the year.
 

Yaakov

Joined Jan 27, 2019
1,612
Can you take photos of what you are working on? How did you determine the component was an LDR? Did you say the housing is black, meaning the entire thing is dark with no clear window?
 

Thread Starter

Sstanier

Joined Mar 4, 2019
17
It’s well and truly in pieces. I worked out it was an LDR by taking it apart to see what it was. It was enclosed in a little black housing I opened - that was why I gave the details in my earlier response.

I have tried replacing the LDR with a new one and still doesn’t work. But my desoldering station died and I am waiting for delivery of a new one so I can’t do anymore until it arrived. I haven’t been able to find a fault yet. According to my multimeter everything is good but I am sure once I really take it apart I will find the fault.

The suggestion from my components store was to use a resistor to close the circuit. Then I can insert a switch into one of the power connections and it should work.
 

Yaakov

Joined Jan 27, 2019
1,612
If the LDR is simply a go/no-go signal, the place to put the switch would be in series with a resistor that simulates the threshold for "go". If somehow it was reversed, and a high resistance is needed, you can make the switch normally closed so pressing it opens the resistor.

The problem here is simply not enough information to give informed advice.
 

djsfantasi

Joined Apr 11, 2010
6,506
If you can measure the resistance of the LDR when lit or dark, as well as measure the voltage (to ground) of both sides of the LDR when lit or dark (four measurements), it possible to use a switch to select between two resistors put in place of the LDR. This may require a SPDT push button switch. Share your results here.
 

Tonyr1084

Joined Sep 24, 2015
4,710
Some questions I have that may be germane to the issue, how does the toy work? By that I mean if you block the LDR does the toy react for a set period of time controlled by the electronics within the toy? Or does it only react during the time the light has been blocked?

Also, if it's LDR, how do you stop the toy from running all night (or all day - depending on its operation)?

In the most general terms, as you already know, an LDR changes resistance with the exposure of light. It shouldn't be too hard to substitute the LDR with a switch and a couple resistors. The two resistors set up a voltage divider (don't worry if this is over your head, you'll catch on). The voltage divider will act like the LDR in the sense that it is now providing an unchanging and constant division in the voltage. Since the LDR requires a change in light levels to cause a change in the resistance, a switch in parallel with one of the two resistors can do the same thing in that when you push the button you change the voltage (same as the LDR will do) and activate the toy.

Before we start throwing schematics at you we need to understand a little more about the toys operation. That's why people are asking for more specific information. If you can manage to get that info to us I'm confident someone here will be able to come up with a brilliant and simple solution to the problem.

Good luck.
 

Tonyr1084

Joined Sep 24, 2015
4,710
Here's a basic idea of how an LDR controlled circuit might work: (see image below)

Light changes the resistance which changes a voltage going to a comparator. Depending on the design the circuit does its thing. If you replace the LDR with the circuit (two resistors and a switch) pressing the button will change the voltage at the comparator the same as it does with the original LDR.

There are two ways of hooking up an LDR, one will drop the voltage the other will increase the voltage, depending on how it's wired. So my proposed change may or may not work. That's why more information is critical to finding a good solution to your problem.

zz LDR.png
 
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